1. Field of the Invention
The present invention relates to a signal processing circuit and a signal processing method of a digital display, which is used in liquid crystal displays and plasma displays and so on, and particularly relates to a signal processing circuit and a signal processing method of a digital display that attempts an improvement of the general versatility of the signal processing circuit.
2. Description of the Related Art
Corresponding to the digitization of broadcasting and data communication, an image display in digital displays are conducted by video signals with an aspect ratio of 4:3, and whose number of pixels in the transverse and longitudinal (horizontal and vertical) directions are 640 by 480, 800 by 600, or 1024 by 768. The image display in digital displays are also conducted by video signals with an aspect ratio of 16:9, and whose number of pixels in the transverse and longitudinal directions are 854 by 480, 1280 by 720, 1366 by 768, or 1920 by 1080. The image display in digital displays are also conducted by digital video signals that are used for general purpose in personal computers, with the number of pixels in the transverse and longitudinal directions being 1280 by 1024.
In digital display panels, such as liquid crystal display (LCD) panels and plasma display panels (PDP) for example, the displaying picture element is classified according to usage, such as VGA (640 by 480 pixels), wide VGA (854 by 480 pixels), XGA (1024 by 768 pixels), or wide XGA (1366 by 768 pixels). For driver integrated circuits (driver IC) that drive the digital display, those with output bits of 2n (n is a natural number), or 1.5 times 2n, which are numbers easy to process digitally, are used.
A driving method to display one horizontal line of video data on a wide VGA panel will be described next. Data for one horizontal line is usually transferred to the display panel using data driver IC's (called “data driver” hereinafter). One horizontal line of the wide VGA panel is composed of 854 pixels, and one pixel is composed of three picture elements, i.e., red, green, and blue elements (RGB), hence data is transferred to 2562 picture elements simultaneously. One picture element of the panel is driven by one output bit of the data driver. Therefore, 41 data drivers are needed when using a sixty-four-bit output data driver, for example. That is because a value of 40.03125 is obtained when dividing the total number of picture elements 2562 by the number of output bits 64, and 41 data drivers are needed to drive a wide VGA panel, because it is not possible to drive all of the picture elements with 40 data drivers. Since 41 data drivers for sixty-four-bit output can drive 2624 picture elements, there are 62 bits (=2624−2562) of data driver outputs that are not connected to the panel, when driving a wide VGA panel with 41 data drivers for sixty-four-bit output. These driver outputs will be called “dummy outputs” hereinafter.
FIG. 1A is a schematic view showing the relation of a panel and a dummy output, and FIG. 1B is an enlarged view of FIG. 1A. A plurality of data drivers 51 are divided into a plurality of groups with three data drivers each, for example, and a tape carrier package (TCP) 52 is allocated to each of the groups. A plurality of bits are outputted from each of the data drivers 51, and some of those bits are made to be dummy outputs 53 that does not get to be connected to panel electrodes. The location of the arrangement of the dummy outputs 53 is usually determined by the arranged relation between the data driver outputs and extracting electrodes of the panel 54, such as the extracting portions of the data electrodes for example. For each of the data drivers 51, display data is inputted from a signal processing circuit 55 into each of the TCPs 52, and the display data is shifted sequentially within the single TCP 52.
In conventional digital displays, dummy output bits are defined for every combination of panel constitution and data driver constitution, and dummy output terminals (called “dummy bits” hereinafter) are allocated at the line memory (not shown) provided inside the signal processing circuit 55, when conducting a digital signal processing for image display.
However, the data driver constitution and the panel constitution, and the picture element pitch in particular, differs between a 42-inch screen display and a 50-inch screen display, even when they are both digital displays displaying the same wide VGA. On account of this, the connections between the data drivers and the panel electrodes are not determined uniquely just because they are wide VGA, and there is a problem in that each of the displays needs to have different dummy bits.
The number of picture elements differ between a wide XGA display and a wide VGA display, even when they are both the same 42-inch screen display, and the number of data driver outputs needed for the wide XGA display is more than those needed for the wide VGA. The dummy bits also differ in such a case. Therefore, there is also a problem in that it is necessary to change the constitution of the circuit conducting the digital signal processing corresponding to the size of the display and the number of picture elements, and also necessary to prepare a signal processing circuit for each model of the display.
These problems are in regard to the relation between the number of picture elements of the digital display in the transverse direction, and the data drivers. But similar dummy bits exist in a relation between the number of picture elements in the longitudinal direction, and the driver ICs for driving in the longitudinal direction, such as scanning driver ICs (scanning driver) or sustain driver ICs (sustain driver) in plasma displays for example, and similar problems are present in these cases also.
Therefore, an exclusive signal processing circuit is needed for each combination of display panel constitution and driver IC constitution. For example, when developing a digital display with a wide variety of products, an exclusive signal processing circuit is needed for each product, and a great amount of development cost and developing man-hours are needed to fulfill this. When either one of the display panel or the driver IC is already developed, and the other one is going to be developed new and combined with the former, there will be a need to develop a large scale integrated circuit (LSI) for the signal processing circuit to realize this new combination, and a great amount of development cost and developing man-hours are needed to fulfill this.